MALFUNCTION INDICATOR LIGHT (MIL)
The MIL is located on instrument panel and is labeled CHECK ENGINE. The MIL will illuminate if the ECM detects a failure of a OBD-II emission related component. When this occurs, a Diagnostic Trouble Code (DTC) will be set into ECM memory.
When a malfunction has been detected in 2 consecutive drive cycles, the ECM will turn on the MIL and store a DTC in memory. One exception is if a misfire malfunction is detected that may damage catalytic converter, the MIL will illuminate or flash immediately and DTC will be set. If the same malfunction is not detected for 3 consecutive drive cycles the ECM will turn MIL off. The DTC will remain in ECM memory for 40 drive cycles, if fault does not recur DTC will be purged from ECM memory.
If MIL remains on during engine cranking, the ECM is not receiving CMP signal or the MIL circuit is shorted to ground. If MIL blinks there may be severe misfire being detected by ECM. To turn MIL off after a repair, an ECM reset command from scan tool must be sent, or 3 consecutive drive cycles must be completed without any detected malfunction. See DRIVE CYCLES. If MIL never illuminates, check MIL circuit for opens and shorts. See WIRING DIAGRAMS article.
FREEZE FRAME DATA
When a DTC is stored, ECM will also record and store engine operating conditions when malfunction occurred. This information is referred to as freeze frame data. Freeze frame data will be stored in ECM memory until cleared, with the exception of the occurrence of an engine misfire or fuel trim malfunction. When a misfire of fuel trim fault occurs, freeze frame data will be updated with the most current information regarding these failures. Freeze frame data cannot be accessed using MIL.
Freeze frame data available is
- Engine coolant temperature.
- Engine speed.
- Vehicle speed.
- Long term fuel compensation (long term fuel trim - displayed as percent).
- Short term fuel compensation (short term fuel trim - displayed as percent).
- Fuel control condition: Open or closed loop.
Malfunction of rear H02S.
- Calculated load value (displayed as percent).
- Diagnostic Trouble Code (DTC) during data recording.
RETRIEVING CODES
- If use of an OBD-II type scan tool is not available, DTCs can be retrieved by changing MIL output from Mode 1 to Mode 2. Mode 1 is the normal malfunction warning mode. Mode 2 displays self-diagnostic results. NOTE: Before switching MIL to Mode 2, perform bulb check (key on engine off). If MIL is inoperative, check and repair MIL circuit as necessary.
- To switch MIL output from Mode 1 to Mode 2, locate and gain access to ECM. See «ECM LOCATION»(ref-17943-S17576166772003082500000) table. Turn ignition on. Using a screwdriver, turn test mode selector fully clockwise. (Scheme 3) After 2 seconds, turn test mode selector fully counterclockwise (back to original position). MIL should now be in Mode 2. When in Mode 2 with key on and engine off, MIL should begin flashing codes NOTE: DTCs retrieved by MIL may also be referred to as flash codes.
- The 4-digit DTCs (flash codes) are read as two 2-digit numbers. The first 2-digit number is indicated by a series of long flashes followed by a series of short flashes. E.g. 1 long flash followed by 2 short flashes indicates DTC 0102. see scheme 4 The DTCs retrieved by MIL are not numerically the same as DTCs retrieved from a scan tool.
- Write down codes and repair in order retrieved. To determine which circuit test to use, see «DTC IDENTIFICATION»(ref-17943-S01111055152002081600000) table. After retrieving DTCs or performing a repair, clear DTCs from ECM memory.
| Application | Location |
|---|---|
| Maxima | Behind Glove Box |
ECM LOCATIONS
Scheme 3
OXYGEN SENSOR MONITOR
- To check if the front (4-cyl.) or left front (V6) oxygen sensor is switching between rich and lean, activate diagnostic test mode 2. See «RETRIEVING CODES»(ref-17943-S36663411692001121700000) under SELF-DIAGNOSTICS USING MIL. Start engine while in mode 2 and run until fully warm. Run engine at 2000 RPM without load for 2 minutes, while monitoring MIL.
- If MIL flashes at least 5 times every 10 seconds, this indicates front oxygen sensor is functioning and fuel mixture is switching between lean and rich. This is an indication fuel mixture control system is okay.
- If MIL stays lit all or most of the time, a lean condition is indicated. Mixture control may be in open loop, ensure engine is fully warm. Fuel mixture may be lean or oxygen sensor may be faulty. Check for DTCs and repair if necessary. Check for conditions that could cause lean mixture, if okay, replace oxygen sensor.
- If MIL is off all or most of the time, a rich condition is indicated. Check for DTCs and repair as necessary. Check for conditions that could cause a rich condition, if okay, replace oxygen sensor.
- To monitor right front (V6) oxygen sensor after monitoring left front oxygen sensor, turn diagnostic mode selector on ECM fully clockwise. Wait 2 seconds, then turn mode selector fully counterclockwise. MIL will quickly flash twice indicating change to right oxygen sensor monitoring. To switch back to left oxygen sensor monitoring repeat procedure. MIL will flash quickly 4 times.
EQUIPMENT HOOK-UP
Ensure scan tool is OBD-II compliant. Turn ignition off. Connect data cable to OBD-II data link connector (located under left side of instrument panel). Plug power cable into cigar lighter. Turn ignition on.
- Ensure engine is warmed to normal operating temperature. If engine does not start, continue with testing. Turn ignition on. Ensure test equipment is properly attached.
- Using the scan tool, select and enter the following data: Select vehicle and engine selection menu. Select year, engine, model and any additional information requested by scan tool. Select ECM. Select DTCs. Select DIAGNOSTIC TEST MODE RESULTS.
- At this point, scan tool should display all DTCs. Write down codes in order displayed. If a communication problem exists between scan tool and ECM, check for loose power and data cables to scan tool. NOTE: If a DTC is retrieved, ECM may have stored data. See FREEZE FRAME DATA ACCESS. If desired, check freeze frame data before clearing codes. Clearing codes will erase freeze frame data.
- To determine if codes will reappear, indicating a hard (non-intermittent) fault, clear codes and recheck for codes. See CLEARING CODES. If DTC immediately returns, malfunction is considered to be a hard fault. If a DTC does not immediately return, vehicle may need to be driven in a special pattern to cause code to reset. See DRIVE CYCLES.
- If one or more DTCs were retrieved, service DTCs in order scan tool displayed them. Go to appropriate DTC test. If no DTCs or DTC P0000 (pass code) were retrieved, proceed to «TESTS W/O CODES»(ref-17959) article.
Pattern "A"
Drive cycle pattern "A" exercises the misfire and fuel system monitors. In drive cycle pattern "A", start engine and let idle (or drive vehicle) until engine coolant temperature reaches at least 158°F (70°F). Turn engine off.
Pattern "B"
In drive cycle pattern "B", EGR and fuel system components are monitored. With engine warm, start engine. Let idle briefly, then drive vehicle up to legal freeway speeds for several minutes. Return to idle and turn engine off.
Pattern "C"
Drive cycle pattern "C" monitors catalyst and other components. Using scan tool, check FREEZE FRAME DATA, for engine speed, engine temperature and calculated load data to recreate. Also for catalyst monitoring purposes, a steady cruise for at least 2 minutes should be achieved.
DATA MONITOR
Data monitor function allows viewing of ECM input and output signals in real time. Turn ignition off. Ensure scan tool is properly connected. Program scan tool using the following steps
- Select vehicle and engine selection menu (optional).
- Select year, engine, model and any additional information requested by scan tool (optional).
- Select GENERIC OBD-II OPTIONS.
- Select DATA MONITOR.
- Turn ignition on or start engine and allow to idle.
- Follow operating instructions from scan tool menu.
- Select input or output signal desired.
FINAL CHECK
- Ensure all electrical components and connectors are hooked-up.
- Test drive vehicle under conditions that may recreate fault.
- Recheck for DTCs.
If symptom or DTC(s) return, ensure ECM terminals are not bent, corroded or damaged in any way. If no fault can be found and symptom or DTC remains, substitute a known-good ECM and retest.
CIRCUIT TESTS
Note. In the following DTC testing, when instructed to perform "FINAL CHECK", see FINAL CHECK .
Check Component
Ensure vacuum system hoses are routed correctly. (Scheme 4) Inspect EGRC-BPT valve and EGR system. See SYSTEM/COMPONENT TESTS article. Repair or replace as required and perform FINAL CHECK.
Scheme 4
Check Input Signal Circuit
Turn ignition off. Disconnect ECM and A/T control unit harness connectors. Using an ohmmeter, check continuity between ECM harness connector terminal No. 6 and A/T control unit harness connector terminal No. 45 (Red wire). If no continuity exists, repair open in Red wire. If continuity exists, check ECM and A/T control unit harness and connectors for damage or corrosion. Repair or replace as necessary and retest system.
SUMMARY
If no DTCs (or only pass codes) are present, driveability symptoms exist or intermittent codes exist, proceed to TESTS W/O CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.